Create temp_dir if not exists

docs/changelog/2770.bugfix.rst

@@ -0,0 +1 @@
+Create default temp_dir.

docs/config.rst

@@ -172,7 +172,7 @@ Core
 
 .. conf::
    :keys: temp_dir
-   :default: {tox_root}/.temp
+   :default: {tox_root}/.tmp
 
    Directory where to put tox temporary files. For example: we create a hard link (if possible, otherwise new copy) in
    this directory for the project package. This ensures tox works correctly when having parallel runs (as each session

src/tox/config/sets.py

@@ -194,6 +194,11 @@ def work_dir_builder(conf: Config, env_name: str | None) -> Path:  # noqa: U100
         def work_dir_post_process(value: Path) -> Path:
             return self._conf.work_dir if self._conf.options.work_dir else value
 
+        def temp_dir_builder(conf: Config, env_name: str | None) -> Path:  # noqa: U100
+            temp_dir = cast(Path, self["work_dir"]) / ".tmp"
+            temp_dir.mkdir(parents=True, exist_ok=True)
+            return temp_dir
+
         self.add_config(
             keys=["work_dir", "toxworkdir"],
             of_type=Path,
@@ -204,7 +209,7 @@ def work_dir_post_process(value: Path) -> Path:
         self.add_config(
             keys=["temp_dir"],
             of_type=Path,
-            default=lambda conf, _: cast(Path, self["work_dir"]) / ".tmp",  # noqa: U100, U101
+            default=temp_dir_builder,
             desc="a folder for temporary files (is not cleaned at start)",
         )
         self.add_constant("host_python", "the host python executable path", sys.executable)

tests/config/test_sets.py

@@ -179,3 +179,11 @@ def test_config_work_dir(tox_project: ToxProjectCreator, work_dir: str) -> None:
     result = project.run("c", *(["--workdir", str(project.path / work_dir)] if work_dir else []))
     expected = project.path / work_dir if work_dir else Path("b")
     assert expected == result.state.conf.core["work_dir"]
+
+
+def test_config_temp_dir(tox_project: ToxProjectCreator) -> None:
+    ini = "[testenv]\nallowlist_externals=touch\ncommands=touch {temp_dir}/foo"
+    project = tox_project({"tox.ini": ini})
+    result = project.run()
+    result.assert_success()
+    assert (result.state.conf.core["temp_dir"] / "foo").exists()